*: refactoring to support streams

when creating a manifest from, or validating, a stream like a tar
archive, it requires thinking about some of the functions differently
than walking a directory tree.

This is the beginning of allowing for such features.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

tar_test.go

@@ -0,0 +1,119 @@
+package mtree
+
+import (
+	"archive/tar"
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func ExampleStreamer() {
+	fh, err := os.Open("./testdata/test.tar")
+	if err != nil {
+		// handle error ...
+	}
+	str := NewTarStreamer(fh, nil)
+	if err := extractTar("/tmp/dir", str); err != nil {
+		// handle error ...
+	}
+
+	dh, err := str.Hierarchy()
+	if err != nil {
+		// handle error ...
+	}
+
+	res, err := Check("/tmp/dir/", dh, nil)
+	if err != nil {
+		// handle error ...
+	}
+	if len(res.Failures) > 0 {
+		// handle validation issue ...
+	}
+}
+func extractTar(root string, tr io.Reader) error {
+	return nil
+}
+
+func TestTar(t *testing.T) {
+	/*
+		data, err := makeTarStream()
+		if err != nil {
+			t.Fatal(err)
+		}
+		buf := bytes.NewBuffer(data)
+		str := NewTarStreamer(buf, append(DefaultKeywords, "sha1"))
+	*/
+	fh, err := os.Open("./testdata/test.tar")
+	if err != nil {
+		t.Fatal(err)
+	}
+	str := NewTarStreamer(fh, append(DefaultKeywords, "sha1"))
+
+	if _, err := io.Copy(ioutil.Discard, str); err != nil && err != io.EOF {
+		t.Fatal(err)
+	}
+	if err := str.Close(); err != nil {
+		t.Fatal(err)
+	}
+	defer fh.Close()
+
+	/*
+		fi, err := fh.Stat()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if i != fi.Size() {
+			t.Errorf("expected length %d; got %d", fi.Size(), i)
+		}
+	*/
+	dh, err := str.Hierarchy()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if dh == nil {
+		t.Fatal("expected a DirectoryHierarchy struct, but got nil")
+	}
+	//dh.WriteTo(os.Stdout)
+}
+
+// minimal tar archive stream that mimics what is in ./testdata/test.tar
+func makeTarStream() ([]byte, error) {
+	buf := new(bytes.Buffer)
+
+	// Create a new tar archive.
+	tw := tar.NewWriter(buf)
+
+	// Add some files to the archive.
+	var files = []struct {
+		Name, Body string
+		Mode       int64
+		Type       byte
+		Xattrs     map[string]string
+	}{
+		{"x/", "", 0755, '5', nil},
+		{"x/files", "howdy\n", 0644, '0', nil},
+	}
+	for _, file := range files {
+		hdr := &tar.Header{
+			Name:   file.Name,
+			Mode:   file.Mode,
+			Size:   int64(len(file.Body)),
+			Xattrs: file.Xattrs,
+		}
+		if err := tw.WriteHeader(hdr); err != nil {
+			return nil, err
+		}
+		if len(file.Body) > 0 {
+			if _, err := tw.Write([]byte(file.Body)); err != nil {
+				return nil, err
+			}
+		}
+	}
+	// Make sure to check the error on Close.
+	if err := tw.Close(); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}